Livestock Production Will Push Earth's Limits

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If demand for meat, poultry, eggs and dairy keeps pace with
projections, by 2050 the environmental consequences of livestock
production could be responsible for 70 percent of the total
greenhouse gas emissions considered a safe threshold for the
planet, new research says.

This leaves little room for all of the other sources of
greenhouse gases, such as transportation and electricity, which
now account for more than 80 percent of emissions.

Livestock could generate an even greater proportion of the
sustainable threshold for other environmental indicators, the
researchers report online today in Proceedings of the National
Academy of Sciences.

"It's sobering," said study lead author Nathan Pelletier who did
the work with Peter Tyedmers while at Dalhousie University in
Halifax, Nova Scotia.

"We're not suggesting that everyone in the world become vegan or
vegetarian," he emphasized. "We really stress the importance of
policies aimed at production and consumption over time by
changing not just how much we eat, but what we eat and how
frequently we eat it."

The pair considered three aspects of global livestock production:
greenhouse gas emissions, biomass consumption and nitrogen
emissions. They looked at estimates of current and future levels
for each of these and compared them with projections for the
Earth's limits, beyond which these systems may become dangerously
or irreversibly out of whack.

For greenhouse gases, a 2006 United
Nations report estimated that livestock production in 2000
produced about 14 percent of global greenhouse gas emissions,
largely via nitrous oxide emissions from fertilizer used to grow
feed and from manure and via digestive methane emissions from
cows and other ruminants.

Meanwhile, many scientists agree that a global average
temperature increase of two degrees Celsius (3.6 degrees
Fahrenheit) is the threshold past which serious and irreversible
negative impacts of climate change are likely to occur.

Based on that threshold and U.N. projections for future global
livestock demand, the team calculated that livestock would
account for around 70 percent of the greenhouse gas emissions in
2050 that would keep the planet below the two degree threshold.

Similarly, Pelletier and Tyedmers determined that future
livestock demand would consume 88 percent of all of the biomass
that humans can safely harvest from the earth's lands.

Humans already are exceeding the third safety threshold, reactive
nitrogen production, according to other researchers. The new
study projects that this threshold would be surpassed by almost
threefold.

Reactive nitrogen is nitrogen that is taken out of its inert form
in our atmosphere and converted into ammonia or nitrate that
plants can use -- either through fertilizer production or by soil
microorganisms.

Exceedingly high levels of this type of nitrogen contribute to
coastal dead zones, smog and acid rain, but "we can't produce
food without it," Pelletier noted.

The team tested a few scenarios to determine how to reduce
livestock's proportion of the future environmental burden.
Switching all beef to more resource-efficient poultry only
reduced impacts by 5 to 13 percent.

Technical improvements such as making fertilizer use and manure
management more efficient will not be enough, the team said.

"If our models are even close and these sustainability thresholds
are right, these technical measures are not going to be enough to
allow us to remain within these sustainability thresholds,"
Pelletier said.

The only scenario the team tested that brought reactive nitrogen
levels below the sustainability threshold by 2050 was one where
humans' recommended protein consumption was provided entirely by
vegetable sources. (The team used soy in their calculations.)

"We stressed that that's not realistic. We chose it in order to
show the range of impacts," Pelletier said.

"Global livestock is an underappreciated point of the global
sustainability problem," Helmut Haberl of the Institute of Social
Ecology in Vienna told Discovery News.

"One of the most important sustainability goals is to feed all
humans," he said. "We have to be sure of that first. At the same
time, when we have one billion undernourished people, we probably
have one billion people who eat too much and particularly too
many animal products. I think we have to face the challenge of
thinking about our lifestyle in terms of what we eat."